1. Field of the Invention
The present invention relates to a method of calculating effective power relating to a capacitor, a method of measuring effective power consumed by the capacitor, a capacitor selection method, a calculator for calculating the effective power consumed by the capacitor, and a recording medium storing the calculation program therefor.
2. Description of the Related Art
Previously, capacitors have been used as electric circuits, such as a snubber circuit of a switching power supply, a horizontal resonant circuit of a color television, and other suitable circuits, in which a desired periodic pulse voltage of a desired waveform other than a sine waveform is applied. In this case, it is necessary to determine an allowable power capacity of the capacitor so as to suppress the heat generated by the capacitor below the allowable capacity, whereby the capacitors do not experience problems (decreased life or destruction due to thermal runaway) caused by self heating due to a dielectric loss. In general, apparent power that can be easily measured is used as the allowable power capacity. This apparent power is obtained by multiplying the effective value of a voltage applied to the capacitor by the effective value of a current flowing into the capacitor. If the waveform of the voltage applied to the capacitor is a sine waveform, the apparent power is easily measured.
However, where a predetermined periodic pulse voltage of a predetermined waveform other than a sine waveform is applied to the capacitor, it is difficult to measure the effective value of the voltage applied to the capacitor and the effective value of the current flowing into the capacitor. Furthermore, since the capacitance and dielectric tangent of the capacitor are dependent on the voltage and frequency thereof, it is difficult to calculate the capacitance and dielectric tangent.
Therefore, Applicants had proposed a method of obtaining apparent power Pa corresponding the original voltage waveform, by Fourier expanding the waveform of a periodic pulse voltage applied to a capacitor in terms of harmonic sine and cosine-wave series of high-order frequency components and calculating the sum of apparent powers Pan for each of the harmonics. This method is disclosed in Japanese Unexamined Application Publication No. 2002-22779 (Patent Document 1).
However, the above-described method disclosed in Patent Document 1 has the following problems.
Effective power Pe consumed by the capacitor is equal to the product of the dielectric tangent and apparent power Pa of the capacitor (effective power Pe=dielectric tangent×apparent power Pa). If the dependency of the dielectric tangent on temperature, voltage, and frequency is low enough to function as a constant, the sum of effective powers Pen calculated for each of the harmonics is equal to the product of the sum of the apparent powers Pan and the dielectric tangent (Σ (effective powers Pen)=dielectric tangent×Σ (apparent powers Pan)). Subsequently, the apparent power Pa may be used as a substitute characteristic of the effective power Pe consumed by the capacitor.
However, if the dependency of the dielectric tangent on temperature, voltage, and frequency is so high that the dielectric tangent cannot function as the constant, the sum of effective powers Pen calculated for the harmonics is not equal to the product of the sum of the apparent powers Pan and the dielectric tangent (Σ (effective powers Pen)≠dielectric tangent×Σ (apparent powers Pan)). Subsequently, the apparent power Pa cannot be used as a substitute characteristic of the effective power Pe consumed by the capacitor.